1. Technical Field
The present invention relates to a semiconductor photoelectrode, a photoelectrochemical cell comprising the semiconductor photoelectrode, and an energy system comprising the photoelectrochemical cell. The present invention also relates to a method for generating hydrogen using the photoelectrochemical cell.
2. Description of the Related Art
A semiconductor material which functions as a photocatalyst is irradiated with light to split water into oxygen and hydrogen.
U.S. Pat. No. 8,236,146 discloses a photoelectrochemical cell and energy system using the same. As shown in FIG. 12, the photoelectrochemical cell 900 disclosed in U.S. Pat. No. 8,236,146 includes: a semiconductor electrode 920 including a conductor 921 and an n-type semiconductor layer 922; a counter electrode 930 connected electrically to the conductor 921; an electrolyte 940 in contact with the surfaces of the n-type semiconductor layer 922 and the counter electrode 930; and a container 910 accommodating the semiconductor electrode 920, the counter electrode 930 and the electrolyte 940. The photoelectrochemical cell 900 generates hydrogen by irradiation of the n-type semiconductor layer 922 with light. In the semiconductor electrode 920, relative to the vacuum level, (I) the band edge levels of the conduction band and the valence band in the surface near-field region of the n-type semiconductor layer 922, respectively, are equal to or higher than the band edge levels of the conduction band and the valence band in the junction plane near-field region of the n-type semiconductor layer 922 with the conductor 921, (II) the Fermi level of the junction plane near-field region of the n-type semiconductor layer 922 is higher than the Fermi level of the surface near-field region of the n-type semiconductor layer 922, and (III) the Fermi level of the conductor 921 is higher than the Fermi level of the junction plane near-field region of the n-type semiconductor layer 922.